The present invention relates to the field of ophthalmology. More specifically, the invention relates to the use of low molecular weight amino alcohols in products for treating contact lenses, as well as other ophthalmic products. The amino alcohols described herein have been found to be useful in preserving ophthalmic compositions. The amino alcohols have also been found to be useful in enhancing the activity of anti-microbial preservatives, and have been found to be particularly effective when combined with borate or borate/polyol buffer systems.
Ophthalmic compositions generally must include an anti-microbial agent to prevent contamination of the compositions by bacteria, fungi and other microbes. Such compositions may come into contact with the cornea either directly or indirectly. The cornea is particularly sensitive to exogenous chemical agents. Consequently, in order to minimize the potential for harmful effects on the cornea, it is necessary to use anti-microbial agents which are relatively non-toxic to the cornea, and to use such agents at the lowest possible concentrations (i.e., the minimum amounts required in order to perform their anti-microbial functions). This balancing of the anti-microbial efficacy and potential toxicological activity of anti-microbial agents is sometimes difficult to achieve. More specifically, the anti-microbial agent concentration necessary for useful preservation of ophthalmic formation or disinfection of contact lenses may create the potential for toxicological effects on the cornea and/or other ophthalmic tissues. Using lower concentrations of the anti-microbial agents generally helps to reduce the potential for such toxicological effects, but the lower concentrations may be less effective for biocidal efficacy of ophthalmic compositions. This weaker activity may create the potential for microbial contamination of the compositions and ophthalmic infections resulting from such contaminations. This is also a serious problem, since ophthalmic infections involving pseudomonas aeruginosa or other virulent microorganisms can lead to loss of visual function or even loss of the eye. Thus, there is a need for a means of enhancing the activity of anti-microbial agents so that very low concentrations of these agents can be utilized without increasing the potential for toxicological effects or increasing the risk of microbial contamination and resulting ophthalmic infections.
Numerous anti-microbial agents have been used or suggested in the art for preserving ophthalmic compositions or disinfecting contact lenses. Such agents have included: benzalkonium chloride (BAC), thimerosal, chlorhexidine, polymeric biguanides, such as polyhexylmethyl biguanides (PHMB), and polymeric quaternary ammonium agents, such as polyquaternium-1. Other agents have included alkylamines, such as the amidoamines described in U.S. Pat. Nos. 5,393,491 (Dassanayake et al.) and 5,573,776 (Dassanayake et al.). While all of these agents have offered some level of utility, their use has also led to certain limitations or drawbacks. For example, thimerosal, which contains mercury, has caused severe ocular irritation resulting from contact lens disinfecting; BAC tends to complex in a detrimental way with negative ionic species typical in ophthalmic compositions and the polymeric biguanides and quaternary ammonium agents, although less ophthalmically irritating/toxic, have limited anti-microbial efficacy against certain species of fungi, including Aspergillus fumigatus and Aspergillus niger. Furthermore, new FDA disinfecting requirements are now being implemented which require even a greater magnitude of microbial kill against a greater number of microorganisms. Thus, a need exists for enhancing the effectiveness of these otherwise useful anti-microbial agents.
Compositions for treating contact lenses and other types of ophthalmic compositions are generally formulated as isotonic, buffered solutions. One approach to enhancing the anti-microbial activity of such compositions is to include multi-functional components in the compositions. In addition to performing their primary functions, such as cleaning or wetting contact lens surfaces (e.g., surfactants), buffering the compositions (e.g., borate), or chelating undesirable ions (e.g., EDTA), these multi-functional components also serve to enhance the overall anti-microbial activity of the compositions. For example, ethylenediaminetetraacetic acid and the monosodium, disodium and trisodium salts thereof (collectively referred to herein as "EDTA") has been widely used for many years in ophthalmic products, particularly products for treating contact lenses. It has been used in such products for various purposes, but particularly for its supplemental anti-microbial activity and as a chelating agent The inclusion of EDTA in contact lens care products and other ophthalmic compositions enhances the anti-microbial efficacy of chemical preservatives contained in such compositions, particularly the efficacy of those preservatives against gram negative bacteria.
Borate buffer systems are used in various types of ophthalmic compositions. For example, two commercial solutions for disinfecting contact lenses, OPTI-SOFT.RTM. (0.001% polyquaternium-1) Disinfecting Solution marketed by Alcon Laboratories, Inc. and ReNu.RTM. Multi-Purpose Solution (0.00005% polyhexamethylene biguanide) marketed by Bausch & Lomb, Inc., contain borate buffer systems which contribute to the disinfecting efficacy of the solutions. An improved borate buffer system for ophthalmic compositions is described in U.S. Pat. Nos. 5,342,620 (Chowhan) and 5,505,953 (Chowhan). That system utilizes borate in combination with one or more polyols, such as mannitol. This combination enhances the anti-microbial activity of compositions, beyond the enhancement obtained with borate alone. However, the present inventors have found that the water soluble complex formed by the borate/polyol also reduces the pH of compositions significantly. As a result of efforts directed to solving this and other problems, the present inventors have discovered that certain amino alcohols can be effectively and safely utilized to provide pH-buffering of ophthalmic compositions and to further enhance the anti-microbial activity of the compositions.
The use of tromethamine in compositions and methods for disinfecting contact lenses is described in U.S. Pat. No. 5,422,073 (Mowrey-McKee, et al.). This publication indicates that a synergistic effect is obtained when tromethamine is combined with other known microbicides and chelating agents. EDTA is identified as the preferred chelating agent.
In view of the foregoing, there is a need for an improved means for enhancing the activity of anti-microbial agents so as to preserve ophthalmic compositions from microbial contamination and disinfect contact lenses more efficaciously. The present invention is directed to satisfying this need.